one-time_pad.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# License: GPLv3
# Date: 20 Novermber 2016
# https://github.com/trizen

# One-time pad symmetric encryption, where the key is pseudo-randomly generated from a given seed.

# See also:
#   https://en.wikipedia.org/wiki/One-time_pad

define READ_SIZE = (2 * 1024**2)    # 2 MB

func usage(err=nil) {
    if (defined(err)) {
        STDERR.say("\n[ERROR]: #{err}\n")
    }
    var name = File(__MAIN__).base
    print <<"USAGE"
usage: #{name} [seed] [<input] [>output]

example:
    #{name} 42 < original.txt > encrypted.dat
    #{name} 42 < encrypted.dat > decrypted.txt

USAGE
    Sys.exit(1)
}

func encrypt(in_fh, out_fh, seed) {

     in_fh.binmode(':raw')
    out_fh.binmode(':raw')

    seed.iseed

    loop {
        var len = in_fh.read(\var chunk, READ_SIZE)
        var key = len.of { 255.irand }.pack('C*')

        out_fh.print(chunk ^ key)
        len == READ_SIZE || break
    }

    return true
}

var seed = Num(ARGV[0] \\ usage("No seed has been specified!"))

encrypt(in_fh: STDIN, out_fh: STDOUT, seed: seed)